Rotary digester



June 23,1942.v J. E. sTEELY ROTARY DIGESTOR Eiled May 25, 1939 l Smm.

Patented June 23, 1942 UNITED STATES PATENT OFFICE ROTARY DIGESTER- James E. Steely, Rosedale, Covington, Va., assignor to West Virginia Pulp and Paper Company, New York, N. vY., a corporation of Delaware Application May 25, 1939, serial No. 275,689

' 2 Claims.

My invention relates to an improved apparatus for making semichemical pulp. The 'principal object of the invention is to provide an apparatus foi` the continuous digestingof wood chips, characterized by simplicity and ease of operation and by high yields.

In the ordinary method of cooking wood for the production of semichemical pulp, resort is had to pressure vessels, which beside being expensive to construct and maintain are not adapted for continuous operation and are Worked on a batch basis. Furthermore, it is necessary to discharge the materials from the ordinary digester into a blow pit and to provide rather elaborate devices for handling the chips up to the pointA where they are `subjected to mechanical disintegration, such devices including me chanical conveyors, washing devices, etc. In my improved apparatus I provide for continuous operation at atmospheric pressure while effecting great simplification in the handling of the materials discharged from the digester by carrying out in the digester itself the separation and preferably the washing of the chips prior to their discharge.

In my improved apparatus the wood or other cellulose-bearing material in the form of chips, sawdust. or other state of subdivision, together with the cooking liquor, e. g., caustic or sulfate liquor suchas is usually employed in the cooking of wood, is introduced into the upper end of a rotary digester maintained at atmospheric pressure, while maintaining the chips and liquor at a cooking temperature as by feeding steam thereto, suitable devices such as a helical vane attached to the inner wall of the digester being provided to propel the cellulosic material and associated liquor therethrough. At the lower end the cooked chips prior to their discharge are preferably washed whereby they are Vdischarged in a state ready for mechanical disintegration, for which purpose a renner of suitable type such as an impact shredder, a ball or rod mill or f jordan may be employed.

If desired, cooking liquor may be added and removed at intermediate points of the digester whereby fresh-cooking liquor may be used in the lower end of the digester, for example, and partially spent liquor used at the upper end.

The invention will be best understood by reference to the following detailed description taken with the annexed drawing, in which Fig. 1 is a view in longitudinal section of an illustrative embodiment; l

Fig. 2 is a similar view of a modification;

Fig. 3 is an enlarged detail of a screening device employed.

In Fig. l, lil denotes the shell of the rotary digester which is mounted and driven in the usual way, as by being supported on the bearings II, i2, and rotated by meansof a ring gear I3, drive pinion I 4, motor I5, such devices thus far described being standard in the art. Chips to be cooked are fed from a bin Il into the rotary through the nozzle I8. Cooking liquor is also added at the top or charging end of the digester through pipe I9. Suitable means are provided for propelling the chips, as by an internal helicoid vane 2i, such vane providing a comparatively narrow open central passage through the rotary to facilitate the passage of steam throughout the rotary when introduced through pipe 23 at the lower end thereof.

When the chips and liquor reach the lower end of the'rotary the liquor is preferably Withdrawn before the chips are discharged. To accomplish this I have provided a stationary housing 25 exterior to the shell l0 and covering a perforated .area or band (perforations 26, Fig. 3) of the shell, such perforated area being lined with a screen 21. Liquor which is withdrawn through the screen 2l and perforations 26 is removed through pipe 30, pump 3|, pipe 32 to, any appropriate means of disposal. Also within the zone of housing 25 the chips are washed by hot water from pipe 35 which has Within the region of the housing 25 a plurality of spray openings, as indicated.

The washed chips are then fed from the rotary preferably into a hopper 36 of a rening engine 31 ofthe impact type driven by motor 38. An end housing 39 to the rotary is provided to prevent back flow of steam from pipe 23 and to conserve heat.

In Fig. 2 a liquor withdrawal zone similar to that described in respect of Fig. 1 is provided approximately in a midsection of the rotary, same comprising a housing 40 over a perforated portion of the shell l0' and a screen 21', the withdrawn liquor being conducted away through pipe 4|. Following the withdrawal of the liquor, fresh liquor is added through pipe 44; housing 45 and perforations 46 in the shell i6'. 'I'he lower end of the rotary is the same as shown in Fig. l, and

similar reference characters are used to desig.

region of the digester. If desired, other zones of withdrawal and admission of liquor may be provided.

The size of the digester may be suitably varied. In operating with a digester 120 feet long and 7 feet in diameter, 3000 to 4000 pounds of chips and 700 to 1000 gallons of cooking liquor may be fed to the digester each hour, approximately 6 hours being required for passage through the digester. A suitable cooking liquor may consist of solutions containing 1A; to l pound caustic soda per gallon and with or without 1/20 to 1/4 pound sodium sulphide per gallon. Other rates of feed of materials and other types of cooking liquors may be employed as will be apparent to those skilled in the art. By means of the steam pipe 2,3 the temperature may be maintained a few degrees short of the boiling point of the liquor. It will be noted that by use of the helical.

vane, chips and liquor associated therewith may be propelled through the digester at any desired rate of speed, depending upon the speed at which the rotary is turned, such vane serving the function of imparting a desired amount of agitation to the chips and liquor while aording a central open core in the digester whereby steam, for example, introduced at either end of the digester will have instant access to the entire contents thereof.

Various vchanges mayfbe made in the apparatus above described without departing from the spirit of my invention or the scope of the appended claims.

I claim:

1. In the manufacture of semi-chemical pulp, an inclined rotary digester comprised of a metal shell for cooking divided raw cellulose-bearing material under atmospheric pressure preparatory to the mechanical disintegration of said material, in combination, vanes internal of said shell and attached thereto permitting agitation and regulating the feed of said material, a device for admitting said material at the charge end of said digester, a spray device for admission of treating liquid adjacent said charge end, a steam conduit for admitting steam adjacent the discharge end and means in said digester for screening and washing the digested pulp preparatory to discharging the same comprising a foraminous portion of said shell, and spray devices for the admission of Washing iluid adjacent said foraminous portion.

2. A digester in accordance with claim 1, having a foraminous portion at the approximate midsection thereof for the withdrawal of spent cooking liquid together with means for the introduction` of fresh liquor between said foraminous sec tion last mentioned and'said foraminous section at the discharge end of the digester, and means for passing liquor discharged at the discharge end of the'digester to the charge end thereof.

JAMES E. STEELY. 

